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  <title>Document</title>
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<body>
  <script>
    var num
    var str1
    //【基本数据类型】  number , string , null, boolean(布尔) ,undefined

    console.log(str1, str2)
    num = 123212343
    var str1 = 'hello'
    var str2 = "world嘿嘿"
    var kong = null
    var b1 = true
    var ud = undefined

    /*
      js用var关键字定义变量，存在【变量提升】
     */

    //【引用数据类型】 arry , object
    var arr1 = [1, 2, 3, 4, 5]
    var obj1 = {
      name: 'lisi',
      age: '66'
    }

  </script>
</body>

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